The present invention relates to a magnetic recording medium and, more particularly, to a magnetic recording medium which is capable of high-density magnetic recording.
In recent years, with the spread of internet, a hard disk mounted on a personal computer tends to have a higher capacity for handling an increased amount of image information. For backing up a large amount of information stored in the hard disk or for allowing such information to be utilized by another computer, various removable recording media are used.
Flexible magnetic recording media such as a magnetic tape and a flexible disk have many advantages that recording and reading of information takes only a short time, that information can be recorded and read by using a small equipment, and the like. Therefore, the magnetic tape and the flexible disk are well used as typical removable-type recording media for backing up the data of a computer and for storing a large amount of data.
It is desired to provide a magnetic recording medium enabling storage of a large amount of data with a smaller number of magnetic tapes or flexible disks and it is desired to further improve the recording density.
The magnetic recording media using a flexible polymer body such as a flexible disk are categorized into an application type and a deposition type. The application type is a type in which magnetic fine particles containing a metal such as iron, chrome, and cobalt are dispersed into a polymer binder and is applied to a substrate. The deposition type is a type in which a cobalt alloy is deposited to form a film in a vacuum environment.
The deposition type magnetic recording medium has a higher recording density than that of the application type magnetic recording medium. However, a magnetic layer used in the flexible magnetic recording medium is a metallic thin film formed by deposition and has a problem of a larger noise than a ferromagnetic thin film to be used in a hard disk which is made of cobalt alloy by sputtering. Accordingly, with a high density recording head using magnetoresistive elements, the magnetic layer can not provide sufficient magneto-electric transform characteristic and is therefore not suited for high recording density performance.
Several attempts have been reported for providing a flexible disk having a ferromagnetic metallic thin-film which is formed by sputtering similarly to the hard disk. However, nothing is in practical use.
In the process of manufacturing the hard disk, a substrate is heated to nearly 200° C. during the sputtering. If the same process is adopted to manufacture the flexible disk, the substrate has poor heat resistance and is thus deformed because the substrate of the flexible disk is generally made of polyethylene terephthalate or polyethylene naphthalate. Even when aromatic polyamide film having excellent heat resistance is used, it is difficult to make a flexible disk with less deformation because the aromatic polyamide film is susceptible to dimensional changes such as thermal expansion, thermal contraction, and humidity expansion.
As a magnetic layer for a hard disk, a ferromagnetic metallic thin film made of a mixture of a cobalt-containing ferromagnetic alloy and a non-magnetic metal oxide has been proposed in JP0573880A and JP07311929A.
The magnetic layer disclosed in JP0573880A and JP07311929A has so-called granular structure in which magnetic particles are dispersed by non-magnetic compound in the magnetic layer. When granular magnetic substance is dispersed in the non-magnetic compound, it is difficult to even the dispersion in size of magnetic particles. When used as a magnetic recording medium, therefore, it has a problem of large noise. Since the magnetic substance is granular, the magnetic substance is susceptible to non-magnetic compound existing around it, has poor structural stability, and hardly applies magnetic anisotropic. Therefore, it is difficult to achieve high coercive force and high output with such a magnetic layer. It is therefore desired to provide magnetic layer which has high structural stability and can resolve the noise problem.